The subject matter disclosed herein relates to ultrasonic inspection. More specifically, the subject disclosure relates to ultrasonic inspection of components having complex geometries and/or contours.
Modern aircraft include many components formed from composites constructed via a layup and cure of a plurality of plies to give the components a selected shape and structural strength. Ultrasonic inspection is typically performed on such components to verify structural integrity of the components and to identify any disbonds, delaminations, foreign object inclusions, etc., in the component. Many other engineering materials also require ultrasonic inspection to verify structural integrity and to identify cracks, seams, stringers, shrinkage, bursts, porosity, lack of fusion, non-metallic inclusions etc. In ultrasonic inspection, an ultrasound transducer connected to a diagnostic machine is passed over the component being inspected. The transducer is typically coupled to the component by a thin layer of couplant (such as water or oil). Often, the transducers are coupled to the component through a water bath, as in immersion inspection. There are two methods of receiving the ultrasound waveform, reflection and attenuation. In reflection (or pulse-echo) mode, the transducer, often a hand-held unit or “hand scanner”, performs both the sending and the receiving of the pulsed waves as the signal is reflected back to the device. Reflected ultrasound comes from an interface, such as the back wall of the component or from an imperfection within the component. The diagnostic machine displays these results in the form of a signal with an amplitude representing the intensity of the reflection and the distance, representing the arrival time of the reflection. The display may also be in the form of a planar or cross sectional image with colors representing reflectors or degrees of signal attenuation. Complex shapes of the component, such as ply drop offs, contours, and curvature mismatches between a front surface (where the transducer is located) and a back surface of the component, make reflection mode inspection of such components difficult at best, requiring constant manipulation of the transducer position in order to monitor the amplitude of the signal reflected from the back wall. Such manipulation results in a less than reliable inspection of the component, such as false positives, false negatives and mislocation of defects, etc.
The present method for scanning components having complex shapes and lacking parallel front and back wall surfaces is through the use of computerized multi axis ultrasonic scanning machines. Sensor scan paths for a component are programmed into a motion controller. Angles of reflection and refraction of the scanning beam in or through the component must be calculated in order to position the ultrasonic sensors properly. Programming the motion controller to scan a complex shaped part is extremely labor intensive.
An alternative method for inspecting complex components is attenuation (or through-transmission) mode. In attenuation mode, a transmitter sends ultrasound through one surface, and a separate receiver detects the amount that has reached it on another surface after traveling through the medium. Imperfections or other conditions in the space between the transmitter and receiver reduce the amount of sound transmitted, thus revealing their presence. Using the couplant increases the efficiency of the process by reducing the losses in the ultrasonic wave energy due to separation between the surfaces. Inspection via attenuation mode is typically performed with the component submerged in an immersion tank, and motion of the transmitter and receiver is controlled via a scan program to inspect selected portions of, or the entire component. Immersion tank equipment is quite expensive compared to equipment required for reflection mode inspection, and further requires development of complex scanning programs for the transmitter and receiver.